ECOLOGICAL CORRELATES OF REGIONAL VARIATION IN LIFE-HISTORY OF THE MOOSE ALCES-ALCES

The food limitation hypothesis of population regulation states that a stable equilibrium will exist between a population and its food resour ces due to a density-dependent decrease in fecundity and/or increase i n mortality. This hypothesis was tested for the moose (Alces alces) by comparing regional variation in life history characteristics in four Norwegian study areas, chosen to represent a gradient both in summer a nd winter range conditions. The rate of body growth was most rapid in the northern study area with the best summer ranges. Lowest body growt h occurred in the population living under the poorest winter condition s. After snow-free winters the rate of body growth increased substanti ally, leading to large annual variations in yearling body masses. Thes e differences in growth lead to significant age-specific differences b etween populations in female carcass masses in autumn. Probability of maturing as a yearling increased with body mass in the three southern populations. In contrast, in the northern study area no such relations hip was found, leading to a delayed age at maturity in the population with the largest females. This shows that the relationship between age at maturity and body mass differs regionally, suggesting different se lective regimes. The peak timing of ovulation of old females in the au tumn showed a latitudinal delay. Females in the alpine population, wit h the poorest winter conditions, had significantly later mean calving dates and produced fewest calves per year. Gestation length appears to be dependent on nutritional condition of females during pregnancy. Mo rtality was highest in the northern study area where most of the death s occurred during the summer. Very few calves died during the winter. These results suggest that a stable high-density equilibrium between m oose and their food resources as expected from the food limitation hyp othesis is unlikely. The decrease in fecundity and the increase in mor tality under poor nutritional conditions during the winter has only a small effect on the population growth rate and is therefore unlikely t o have a strong regulatory effect. In the absence of large predators, this will lead to large fluctuations in population size that will over shoot the carrying capacity.